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Trans-vaginal sonography is the procedure of choice in evaluating the viability of embryos early in pregnancy. Previous reports have shown that trans-vaginal sonography can identify early pregnancy with confidence, correlating certain growth parameters of the pregnancy with the menstrual history.
The term ”viability” implies the ability to live independently outside the uterus and, strictly speaking, cannot be applied to embryonic and early fetal life. However, this term has been accepted in ultrasound jargon to mean that the embryonic or fetal heart is seen to be active and this is taken to mean the conceptus is alive.
The measurements of embryonic length and heart rate (HR) and those of the gestational sac diameter (GSD) and yolk sac diameter (YSD) have been used for assessment of gestational age (GA) and prediction of adverse pregnancy outcome, such as miscarriage.
Some previous studies tried to find the predictability of each parameter but results were different among studies.
In this current study; trans-vaginal ultrasound was done measuring to 233 pregnant women with pregnancy of uncertain viability. Mean gestational sac diameter, yolk sac diameter and crown rump length were the parameters studied.
The inclusion criteria were pregnancy of uncertain viability in the study period, gestational age by the menstrual period < 84 days, and finding at trans-vaginal sonography of one of a single intrauterine gestational sac with mean sac diameter < 20 mm and with no visible embryonic structures (empty sac(, single intrauterine gestational sac containing an embryonic pole with maximum length < 6 mm and no embryonic heart pulsation (small embryo) or a single intrauterine gestational sac with mean sac diameter < 25 mm and a visible yolk sac but no visible embryonic pole (yolk sac only).
The exclusion criteria were women who will undergo termination of pregnancy or women with multiple pregnancies.
Before being admitted to the clinical study, all enrolled women consented to participate after the nature, scope, and possible consequences of the clinical study had been explained in a form understandable to them. Only their numbers and initials were recorded.
There was a statistically significant result of mean gestational sac diameter with a positive fetal echo inside to consider the cut-off value of 15.2 mm as a good positive predictor of fetal viability.
Regarding mean gestational sac diameter in the absence of fetal echo inside, crown rump length, yolk sac diameter, there was no statistically significant result of any diameter of each to be considered as a good predictor of fetal viability.For the mean gestational sac diameter in all pregnant women involved, the best cut-off value was 20.9 mm (+ve LR=8.3, -ve LR=0.9). The area under the curve for this parameter was 0.625 with a confidence interval (0.5-0.7).For the mean gestational sac diameter in the pregnant women where no fetal echo was present at the first scan, the best cut-off value was 20.9 mm (+ve LR=8.9, -ve LR=0.93). Area under the curve for this parameter was 0.594 with a confidence interval (0.5-0.7).For the crown rump length and the yolk sac diameter, no single value for these two diameters could be considered as a cut-off value.
Concluding our results, the use of logistic regression model did not allow prediction of pregnancy viability in pregnancies of uncertain viability. Mean gestational sac diameter was the only parameter having a significant effect on the outcome with cut-off values of 20 mm generally and if the sac was empty and 15 mm if there was a fetal echo inside.
These results are corresponding with many recent literatures trying to support conservative management to stop termination of pregnancies that may be viable. As all parameters are inconclusive, follow-up scan is recommended in most guidelines with conflict about the interval between first scan and follow up scan.